Project - Geology
The geological setting of the Casino deposit is typical of many porphyry copper deposits.
The deposit is centred on the 70-million-year-old, east-west elongated porphyry stock called the Patton Porphyry. The Patton Porphyry intrudes older, surrounding rocks from the Dawson Range Batholith and Paleozoic schists and gneisses of the Yukon Tanana Terrane. Intrusion of the Patton Porphyry caused brecciation (break-up, fragmentation) of both the earlier intrusive rocks and surrounding country rocks along the northern, southern, and eastern contacts of the stock, resulting in contact breccias (rocks made of rock fragments cemented by a fine-grained matrix) Brecciation is best developed in the eastern end of the stock where the brecciated zone is up to 400 m wide in plain view. To the west, along the north and south contacts, the breccias narrow gradually to less then 100 m. The overall dimensions of the intrusive complex are approximately 1.8 by 1.0 km.
Primary copper, gold, and molybdenum mineralization was deposited from hydrothermal fluids that exploited the contact breccias and fractured wall rocks. Higher grades occur in the breccias and gradually decrease outbound from the contact zone, both towards the centre of the stock and outward into the granitoids and schists.
The Casino deposit is unusual amongst Canadian porphyry copper deposits in having a well-developed, enriched blanket of secondary copper mineralization similar to that found in deposits in Chile and the southwestern US. Unlike other Canadian porphyry deposits, the Casino deposit’s enriched copper blanket was not eroded by glacial action.
At Casino, weathering during the Tertiary Period leached the copper from the upper 70 m of the deposit, forming the leached cap, and re-deposited it lower in the deposit, forming the supergene enrichment zones. This created a layer-like sequence consisting of an upper leached zone up to 70 m thick, where all sulphide minerals have been oxidized and copper removed, resulting in a bleached, limonitic leached cap containing residual gold. Beneath the leached cap is a zone up to 100 m thick of secondary copper sulphide mineralization, primarily underlying the leached cap.
The copper grades of the enriched, blanket-like zone can be up to twice that of the underlying un-weathered hypogene zone of primary copper mineralization, the latter comprising pyrite, chalcopyrite and lesser molybdenite. The hypogene copper mineralization is persistent at depth, extending more than 600 m below surface, and beyond the deepest drill holes.
For more information about the proposed Casino Mine Project’s geology and deposit type, please view the 2022 Feasibility Study.